Such a coupling is known from, e.g., European patent application 0 270 302, which describes a coupling for a liquid product packaging and dispensing assembly in which liquid is pumped from a container via the coupling through a tube to the point of use. The coupling has a first interconnectable member with a hollow post and a biased sleeve closing openings in the hollow post and a second interconnectable member with a hollow sheath and a biased piston closing an opening at the end of the sheath. The parts are configured so that, upon connection, the post unseats the piston while the sheath displaces the sleeve, thereby allowing liquid flow. In one form, the container may be collapsible and is preferably situated inside a box for convenience during storage and transport. EP 0 270 302 mentions that a problem arising with such containers resides in that upon uncoupling the container from the tube, residues of the liquid which has been flowing through the coupling between them are apt to be spilled. This can be hazardous if the liquid is noxious, for example if the liquid is a very alkaline product such as industrial mechanical dishwashing liquid. The coupling according to EP 270 302 indeed has the advantage that when it is disconnected both hollow bodies are sealed, and that it reduces or even obviates spillage. Obviously, a close fit of the sheath around the post is valuable for avoiding spillage upon disconnection. However, it appeared that the tight seal provided by the couplings in hand deteriorates during prolonged use. As a result, the couplings start to leak and must be replaced or overhauled prematurely, i.e. while, apart from the parts responsible for the close fit, all the other parts are still in perfect working order. The invention aims to provide a coupling of the above-mentioned type which allows leak-tight connection and disconnection over a period of several years of normal use.